Precise Determination of Hydrostatic Pressure Correction Coefficient of Triple Point Cell of Water using Cryogenic Current Comparator Bridge

Abstract

Applying a cryogenic current comparator bridge to resistance thermometry, the temperature distributions along the thermometer wells of two triple point cells of water are precisely measured using a standard platinum resistance thermometer with low measuring currents of about 0.1 mA. The average hydrostatic pressure coefficient of the two cells calculated from the temperature distributions is -0.854(38) mK/m. This value agrees well with the reported value of -0.856 mK/m, but is not consistent with the recommended value of the International Temperature Scale of 1990, -0.73 mK/m.

Automated system for measuring temperature profiles inside ITS-90 fixed-point cells

“…The data are weighted at 0 mm and 80 mm as a result of the measurement procedure. The slope of the linear fit curve is −0.9 mK m −1 , which deviates from the literature value of −0.73 but it is in good agreement with the results presented in [4] where the hydrostatic pressure coefficient was found to be −0.854(38) mK m −1 (represented with a thin solid line). The uncertainty due to the difference between the ideal and measured immersion curves is 13 µK, calculated as a standard deviation of residuals between the fitted linear curve and the theoretical value, over the bottom 80 mm.…”